The present invention relates to an optical fiber capable of having an optical signal evanescent-field easily coupled, and systems constructed therewith.
Various proposals have heretofore been made for forming optical fibers whose evanescent-field is readily coupled. In particular, a known type of geometry previously proposed is that one wherein a cladding which surrounds an optical fiber core has a substantially D-shaped profile, as disclosed in U.S. Pat. Nos. 4,589,725; 4,669,814; 4,387,954; 3,887,264; and 3,823,997, the disclosures of which are incorporated herein by reference. However, a common disadvantage of the D-shaped fibers constructed according to the teachings of these patents is that the fibers tend to be unduly lossy and accordingly not of significant practical use in view of the rather high attenuations thereof.
Accordingly, it has also been proposed to form D-sections in otherwise cylindrical fibers at localized regions for localized coupling, as disclosed in U.S. Pat. Nos. 4,386,822 and 4,054,366, the disclosures of which are incorporated herein by reference. However these proposals have the disadvantage that removing a portion of a cladding of an optical fiber at a localized section is an extremely craft sensitive operation in view of the extremely small diameter size of the cladding, e.g. on the order of 100-200 microns, and accordingly such procedures are not readily adaptable for use by a relatively untrained craftsman in outside plant environments.